Selling my PSA 7.5" 300AAC BLACKOUT 1/8 PHOSPHATE 6" LIGHTWEIGHT M-LOK UPPER WITH BCG & CH with less than 200 rds through it. Also comes with magpul flip up sights and 80 rds of subs. For $450
Forgive the noob question, new to the AR platform, will these uppers mount to any AR15 lower? Is there anything specific someone with an AR15 would need?